Vapor degreasing system

ABSTRACT

Items to be cleaned of rosin are confined within the vapor end of a refluxing chamber. A two-phase liquid solvent system is contained in the bottom of the chamber. The solvent system comprises an aqueous solution of a base of sufficient strength to saponify the organic acid on the items to be cleaned, and an organic solvent immiscible with the aqueous solution. The solvent is boiled and forms a vapor phase consisting of the vapors of the organic solvents and water vapor, which vapor phase contacts the enclosed item. The base, being of low volatility, does not vaporize. The organic solvent dissolves the rosin and, by condensation, the solution of rosin in organic solvent drips back into the turbulating liquid phase where it is contacted by the base. The base saponifies the rosin; the resulting soap is the waste of the process. The soap dissolves in the water, and the organic solvent is available again in the cleaning system. The water and water vapor dissolve any other salts present as a contaminant in the rosin and carry such contaminants back into the turbulating liquid phase.

United States Patent 1 l 111 B 3,923,541

Healy 1 Dec. 2, 1975 i 1 VAPOR DEGREASING SYSTEM Primary ExaminerS. Leon Bashore [75] Inventor: Robert Michael Healy, Warrenville, Assistant E'mmi"e' Marc Caro In. Attorney, Agent, or Firm-Ronald M. Goldman [73] Assignee: Litton Systems, Inc., Chicago, Ill. [22] Filed: June 20, 1973 [57] ABSTRACT [211 App. No: 371,836 items to be cleaned of rosin are confined within the vapor end of a refluxing chamber. A two-phase ilqLllCi Published under the Trial Voluntary Protest solvent system is contained in the bottom of the cham- Program on January 28, 1975 as document ber. The solvent system comprises an aqueous solution B 37 l 3 of a base of sufficient strength to saponify the organic acid on the items to be cleaned. and an organic sol- U-S. Cl. ent the aqueous solution The so]. 134/105; 134/108; 252/369 vent is boiled and forms a vapor phase consisting of Int. Clthe vapors of the rganic olvents and water vapor of Search 35, 40, 3O, 1O, vapor phase contacts the enclosed item The 134/11, 1081252/369, 6, 364 base, being of low volatility, does not vaporize. The

organic solvent dissolves the rosin and. by condensal l References Cited tion, the solution of rosin in organic solvent drips back UNITED STATES PATENTS into the turbulating liquid phase where it is contacted 2,1 l3,l29 4/l938 Dinley l34/l1 by the base- The base sapohifies the rosin; the result- 2 2g5 333 9 3 Humphmy 252 3 9 X ing soap is the waste of the process. The soap dissolves 3,070,463 12/1962 Barday 134/11 in the water, and the organic solvent is available again 3.0859 8 4/1963 Sh i t al- 134/30 in the cleaning system. The water and water vapor dis- 3,094.469 6/1963 Strauss et al..... 134/40 X solve any other salts present as a contaminant in the 3,733.218 5/1973 Begun l34/4OX rosin and carry such contaminants back into the turbulating liquid phase.

1 Claim, 1 Drawing Figure US. Patent Dec. 2, 1975 3,923,541

VAPOR DEGREASING SYSTEM FIELD OF THE INvENTIoN This invention relates to an improved two-phase vapor degreasing system and, more partieularly,,-to an improved vapor degreasing system in which the major part of the resulting waste products is biodegradable.

BACKGROUND OF THE INVENTION A wide variety of manufactured items, for example, printed circuit boards, electronic components, and machined parts and assemblies, pick up contaminant residues during manufacture, storage, or use. These contaminant residues can be of an ionic type, a non-ionic type, or both. These items thus require cleaning and a vapor degreaser is commonly used to do so. I

A vapor degreaser or vapor degreasing -system,"as otherwise termed, includes a covered vat or other closed chamber, sometimes technically referred to as a refluxing chamber, containing a liquid solvent. The items to be cleaned are placed in the upper portion of said chamber and the solvent is heated to-form a solvent vapor within the upper part of the chamber above the turbulating liquid. The vapor dissolves the residues on the item and effectively washes such residues from the confined items; the condensate drips down into the liquid phase. The cleaned items are thereupon removed from the chamber. Various means are known for automatically inserting and removing items and for automatically heating the liquid solvents. The reader may make reference to the literature for the details of their.

construction and operation inasmuch as such ancillary devices are not necessary to an understanding of how to make and use the disclosed invention andarenot further herein described.

Many types of vapor degreaser solvent formulas are available for use in vapor degreaser systems. The advertisers of some of these solvents-claim that their solvent has the property of dissolving both organic and inorganic residues. Such solvents, however,-are generally found to contain an alcohol as the polar solvent. And alcohols are rather poor solvents for many ionic compounds. The efficiency of those particular solvents for cleaning ionic compounds is therefore low.

Many existing solvents, moreover, can be reclaimed, and, typically, this solvent reclamation is accomplished by use of a distillation process. After distillation, however, an insoluble residue remains in the bottom of the refluxing chamber, referred to asthe sump, which obviously presents a waste disposal problem. This is particularly true in that such residues are not biodegradable and may not be flushed into the local sewer systems,

In one prior art degreasing system disclosed in US. Pat. No. 3,085,918, granted Apr. 16, 1963, a degreasing system is disclosed in which the part to be cleaned is treated in a two-phase liquid system containingessentially a chlorinated hydrocarbon, for example trichloroethylene, perchloroethylene, methylene chloride or I l l -tricholoroethane containing a small amount of cationic surface active agent and a proportion of water. That process also leaves a waste in the organic phase which is not biodegradable.

Various aqueous cleaners or solvents do appear on the market which convert resinous acids to watersoluble biodegradable soaps. The disadvantage of these solvents is that they cannot be used in a vapor degreaser to vapor clean. The parts to be cleaned must be in contact 2. with the. liquid phase of the'solvent. Typically such a solvent is used in a washing machine" type of operation in which the item to becleaned is immersed in turbulent solution whic-hwashes and dissolves the residue.

: i f'oBJ cTs oETHE INVENTION Accordingly, it is an object of my invention to provide a vapor degreasing solvent that results in a biodegradable water-soluble waste product.

- And it is an additional object of my invention to provide a vapor degreasing system having a two-phase liquid solvent capable of converting rosin residues into a biodegradable water-soluble soap.

BRIEF SUMMARY OF THE INvENTIoN In accordancewith the foregoing objects, the vapor degreaser solvent system of may invention exists in two phases in the liquid state: an aqueous phase, comprising water and a base of-low volatility of sufficient strength to saponify the organic acid to be removed from the object to be cleaned; and an organic solvent liquid immis cible with water, which may be a halogenated hydrocarbon or mixture thereof. Minor amounts of anti-foam agents and volatile wetting agents, such as alcohol, may be included. Additionally, aliphatic hydrocarbons may be included in the organic solvent to alter the boiling temperature of the solvent system.

Futher, in accordance with another aspect of my invention, the solvent system is placed in a refluxing chamber and the system is heated and turbulated to form a vapor phase comprising the organic compounds and some water'vapor, but not the base, which is of low volatility and does not vaporize. The vapor wets the contaminated parts, installed in the upper part of the refluxing chamber and the organic solvent thereby dissolves the rosin or other organic compounds and the water dissolves any salts or inorganic acids; the condensate drips back into the-turbulating liquid. In the liquid phase, any acid present comes in contact with the base and thence chemically combines with the base to form a salt or soap-The soap, soluble in water, dissolves in the water contained within the two-phase liquid system. Conveniently the soapy water may be drawn off and disposed ofin the utility sewer system.

The foregoing objects and advantages characteristic of my invention become more apparent from a consideration of the detailed description of my invention which follows taken together with the FIGURE of the drawing which illustrates a preferred embodiment of my vapor degreasing system.

DETAILED DESCRIPTION OF INVENTION A closed chamber I, sometimes termed a refluxing chamber, is illustrated symbolically in the FIGURE. The chamber is closed with a cover 2 and a tray 3 is suspended by wires 4 from the cover. An item to be cleaned 5, such as a circuit board, is placed on the tray.

The chamber is filled to a predetermined depth with the liquid cleaning solvent system 7, which is in two phases, 7a and 7b, as becomes more apparent, so as to leave unfilled the upper portion of the chamber. A source of heat, represented symbolically by a heating rod, which is a conventional electric heating device 9, is provided. A condensing coil 6 is conventional structure is included in the upper part of the chamber. The condensing coil is typically hollow metal tubing and a source -of coolant, not illustrated, pumps coolant through the tubing to enhance condensationv This device removes heat from the vapor, thus permitting a high condensation rate. A reservoir for replenishing solvent is shown symbolically as 8. The reservoir is connected by piping, illustrated by lines through a valve 11, to chamber 1. A settling vessel 12, a slight modification to a conventional degreaser, is connected by a pipe 13 and valve 14 to one part of the chamber containing phase 7a and is connected by pipe 15 and valve 16 to a lower part of the chamber, containing phase 7b. An outlet pipe 17 is located in the upper part of settling tank and a valve 18 closes the pipe.

It is clear that the refluxing chamber and associated plumbing is illustrated only symbolically and with the simplest elements necessary to define a basic vapor degreaser system. Inasmuch as those details of conventional vapor degreasers and plumbing of various types are known to those of ordinary skill in the art and are not necessary to an understanding of my invention, they need not be illustrated or described in detail here. However the reader may make reference to the literature should he desire to consider a vapor degreaser in detail.

Liquid solvent 7 is a two-phase liquid solvent in that it comprises at least two liquids which are immiscible in one another and whichin the quiescent state separates into two phases or layers, 70 and 7b. As brought out more fully hereafter, liquid layer 7b is an organic cleaning solvent substantially immiscible in water. This phase contains halogenated hydrocarbons, which are insoluble in water, and, by way of example, commercially available dichoromethane, tetrachloroethylene, trichloromonofluoromethane, trichlorotrifluorethanes, and tetrachlorodifluoroethanes. Liquid layer 7a is largely water and a strong organic or inorganic base of low volatility, such as an alkali metal or alkaline earth metal hydroxide, diethanol amine, or an alkali metal silicate or carbonate. In addition, as hereinafter described, in certain examples liquid phase 7a may contain additionally additives which reduce foaming and for other purposes.

As is conventional in a vapor degreaser, the item to be cleaned of contaminants. such as rosin or resin, is inserted on the tray 3 and is therein suspended above the liquid solvent 7. The container is covered so as to prevent the escape of vapors. In operation heater 9 is operated to heat the contents of the chamber 1 and the liquid solvent 7 is brought to a boil. The liquid 7 is thus turbulated so as to intermix the two phases, 7a and 7b, and a portion of the cleaning liquid 7 is vaporized. The vapor consists primarily of the organic solvent from phase 7b and some parts of water. Inasmuch as the base is of low volatility it remains in the turbulating liquid solution and does not vaporize.

The organic solvent vapors condense upon item 5 and dissolve any rosin residues thereon. The water vapor or vapor of any other polar compound, such as alcohol, as may be present aids in dissolving any salts present as a contaminant in the rosin.

The condensed solvent containing the dissolved impurity drips back into the turbulating liquid phases 7 and thence comes into contact with the base. Assuming the contaminant to be an organic acid, such as resin or rosin referred to above, the base chemically reacts with and saponifies the rosin, forming an organic salt, commonly termed a soap.

The soap is soluble in water and accordingly this in turn is dissolved in the aqueous phase of the turbulating liquid.

As desired thereafter the solvents 7 may be allowed to cool and separate again into two layers, 7a and 7b in the settling chamber. The aqueous phase may be drawn off via the settling chamber 12 as necessary to remove the soap and dissolved salts. For example, the valves 14 and 16 are opened to allow the liquid phases to fill the settling tank 12 and the valves are again closed. Then valve 18 is opened to allow a part of the liquid phase 7a to run out outlet 17. The major part of drawn-off solution is of low toxicity, is biodegradable, and is miscible with ordinary water. Accordingly it may be deposited in the utility sewer system. The organic solvent remains in the vapor degreaser. Additional aqueous phase may be added when necessary to replenish the portions drawn off. And, occasionally, the small losses of the organic phase due to drag out and vapor loss may be replenished.

The two-phase liquid solvent used in my invention is further illustrated by the following examples. In some of the examples which follow the rosin is inserted as a contaminant residue directly into the liquid for ease of experiment. The action of the rosin is thus speeded up. However those examples serve as a valid demonstration of the solvent as applied in a vapor degreaser.

EXAMPLE I ml of 15 volume percent n-propanol in water,

150 ml difluorotetrachloroethane,

5.6 grams potassium hydroxide, and

the contaminant, 15 grams WW grade gum rosin, were mixed in a round bottom glass flask and covered. The flask was covered and the mixture was refluxed for a period of approximately 8 hours. Thereafter the mix ture was cooled and allowed to settle whereupon the liquids separated into two phases or layers of liquid. The upper layer was clear brown in color. The lower layer was water white. The pH factor of the upper lay was Ca. 12.8. As is apparent, this demonstrates that the rosin was dissolved and had been quantitatively saponified and transferred to the aqueous phase in accordance with the operation previously described.

EXAMPLE 2 45 ml of difluorotetrachloroethane,

45 ml of water,

1.68 grams potassium hydroxide,

0.5 ml of 10 volume percent of Surfynol-44O in npropanol, and

the contaminant, 6.7 grams WW rosin, were placed in a round bottom glass flask and covered. The contents were heated, brought to a boil and allowed to reflux for a period of approximately 8 hours. The boiling point of the mixture was 76 Centigrade. Thereafter the solution was allowed to cool and settle and the liquid thereupon separated into two layers or phases. The upper phase was colored clear brown. The lower phase was colored water white. The pH factor of the upper layer was 12.6. This also demonstrates that the rosin placed into the mixture was dissolved and had been quantitatively saponifled and transferred to the aqueous phase.

EXAMPLE 3 50 ml of trichlorotrifluoroethane,

50 ml of water,

1.68 grams potassium hydroxide,

0.5 ml 10 percent (vol) Surfynol-44O in n-propanol,

and

the contaminant, 6.8 grams WW rosin,

were mixed in a round bottom glass flask and covered. The flask was placed upon a heater, the contents were brought to a boil and were refluxed for a period of approximately 6 hours. Thereupon the flask was removed from the heater and the contents allowed to cool and settle. Thereafter the contents separated into two distinct layers. The upper layer was a clear brown color and had a pH factor of 12.8. The bottom layerwas water white in color.

EXAMPLE 4 50 ml of monofluorotrichloromethane,

50 ml of water,

1.2 grams sodium hydroxide,

0.5 ml 10 volume percent Surfynol-44O in n- ;propanol, and

the contaminant, 6.8 grams WW rosin were placed in a round bottom glass flask and covered. This mixture was shaken until the rosin dissolved. On settling, the upper layer was clear brown in color and the lower layer was water white. This example demonstrates that although monofluorotrichloromethane has too low of a boiling point to use alone, it can be used in small amounts with other solvents to lower the boiling point.

EXAMPLE 5 24 ml of diethanol amine diluted to 200 ml with water,

200 ml tetrachloroethylene, and

41.2 grams WW rosin were mixed in a round bottom glass flask and covered. The contents were heated and refluxed over a period of approximately 8 hours. Thereupon the contents were cooled and allowed to settle. The contents thereupon separated into two layers and an analysis showed an equilibrium ratio of 0.69 of rosin in the upper layer to rosin in the lower layer. This example shows that a strong organic base can be used in the solvent in place of the inorganic base. As with other bases, not fully ionized, the organic phase will always contain some rosin after initial use.

EXAMPLE 6 147 ml of tetrachloroethylene,

108 ml of n-propanol, and

45 ml of water were mixed and placed in the bottom of a Soxhlet extractor. Forty-eight grams of WW rosin was placed in the upper chamber of the extractor. The liquid mixture 'was heated to the boiling point and allowed to reflux for a period of about 1 hour. During that time the rosin completely dissolved. In this last example it is noted the inorganic base is omitted, much as appears in prior art solvents, but that rosin cleaning is still carried out. However the rosin remains in the organic phase and is not saponified, thus the waste is not biodegradable.

EXAMPLE 7 18.1 gm of Na Si O .9H O

0.5 ml methyl alcohol with 10 percent Surfynol-44O diluted to 50 ml with water 5 ml heptane 45 ml tetrachlorodifluoroethane 6.8 gm rosin Refluxed 1.5 hours. Brown color of upper phase shows considerable rosin has been transferred to aqueous 6 phase. This again shows non-fully ionized bases can be used. i I

v EXAMPLE 8 1.68 gm KOH 0.5 ml n-propanol 3 drops oleyl alcohol diluted to 50 ml.

50 ml trichlorotrifluoroethane 6.8 gm rosin Refluxed; liquids boiled without excess foaming, showing olely alcohol can be used as anti-foam agent.

EXAMPLE9 50 ml water 6 ml diethanol amine 6.8 gm rosin 3 drops of Dow DE 31 50 ml dichloromethane Refluxed mixture overnight. Reflux temperature was 37.8 C. The pH of the aqueous layer after cooling was 10.1. Placed this refluxed mixture in small vapor degreaser with two printed circuit boards which had been rosin-flux coated and partially clipped in solder. The boards were quickly cleaned by the vapors of the mixture, showing the latter to be still efficient after saponifying considerable rosin.

The system may also contain anti-foam agents, well known to those versed in the art, and as such commercially available.

In the same manner volatile wetting agents such as alcohols, may be added to enhance the action of the degreasing system. Both of these types of additives, present in minor amounts, are distributed between the two phases in various proportions according to their specific solubilities. In addition the organic phase may contain aliphatic hydrocarbons such as hexane, heptane, etc. These are useful to alter the boiling temperature of the system, and the melting point of organic solvent. They are also, in general, less costly than the halocarbons and should be used in proportions small enough so that the system does not become flammable.

The base used in the foredescribed system must be strong enough to neturalize the acid contaminant being washed down into the sump. For example. the dissociation constant of abietic acid, the main constituent of rosin, has been reported only as 10- in percent methanol; in water it would be stronger, If we use the available data for the acid and Kb=l0 for the carbonate ion, the reaction should go:

(a silicone anti-foam agent) H. Abiate H abiate H CO; HCO;

'7v move some, but not all, the rosin from the organic phase. They would remove a greater portion of stronger acid contaminants. Silicates are slightly stronger bases than carbonates, and remove more rosin. Organic bases, such as diethanol amine, remove more than either of the two bases mentioned, even when they are not as strong bases. This may be due to some solubility of the amine in the organic phase. Bases such as sodium or potassium hydroxide remove rosin quantitatively from the organic phase. The base should, additionally, have good solubility in the aqueous phase and be substantially involatile under the refluxing conditions.

in many of the foregoing examples the aqueous phase, water, included amounts of foam-reducing additives and wetting agents such as n-propanol. The organic layer had various examples of solvents which may generically be termed halogenated hydrocarbons and suitable hydrocarbon additives. The base, which was mixed with the water, is of low volatility. Essentially the base employed must be strong with respect to the organic salt, the soap, which is to be formed upon a combination of the base with the organic acid, such as rosin.

What I claim is:

1. The method of cleaning an article contaminated with organic acid materials so as to form a biodegradable waste comprising the steps of:

inserting the article to be cleaned of organic acid res idues into the vapor section of a vapor degreaser. said vapor degreaser having a two-phase liquid solvent located in the sump thereof, said two-phase liquid solvent comprising a first liquid containing an organic solvent and a second liquid containing water and an inorganic base of low volatility, said inorganic base being sufficiently strong to neutralize said organic acid materials, and said first and second liquids being immiscible in one another; heating said mixture to boil said two-phase liquid solvent wherein said solvent is in a state of turbulance and a vapor of water and organic solvent is created in said vapor section and refluxing said mixture,

without vaporizing said inorganic base. 

1. THE METHOD OF CLEAINING AN ARTICLE CONTAINED WITH ORGANIC ACID MATERIAL SO AS FORM A BIODERGRADABLE WASTE COMPRISING THE STEPS OF: INSERTING THE ARTICLE TO BE CLEANED OF ORGANIC ACID RESIDUES INTO THE VAPOR SECTION OF A VAPOR DEGREASER, SAID VAPOR DEGREASER HAVING A TWO-PHASE LIQUID SOLVENT LOCATED IN THE SUMP THEREOF, SAID TWO-PHASE LIQUID SOLVENT COMPRISING FIRST LIQUID CONTAINING AN ORGANIC SOLVENT AND A SECOND LIQUID CONTAINING WATER AND AN INORGANIC BASE OF LOW VOLATILITY, SAID INORGANIC BASE BEING SUFFICIENTLY STONG TO NEUTRALIZE SAID ORGANIC ACID MATERIAL, AND SAID FIRST AND SECOND LIQUIDS BEING IMMISCIBLE IN ONE ANOTHER; HEATING SAID MIXTURE TO BOIL SAID TWO-PHASE LIQUID SOLVENT WHEREIN SAID SOLVENT IS IN A STATE OF TURBULANCE AND A VAPOR OF WATER AND ORGANIC SOLVENT IS CREATED IN SAID VAPOR SECTION AND REFLUXING SAID MIXTURE, WITHOUT VAPORIZING SAID INORGANIC BASE. 